A multi-cell power converter includes a plurality of first converter cells coupled to an input and a plurality of second converter cells coupled to at least one output. During normal operation of the multi-cell power converter, each of the first converter cells charges a corresponding DC link capacitor and each of the second converter cells receives power from a corresponding DC link capacitor to provide an output power at the at least one output.
During normal operation of the multi-cell power converter, the first or second converter cells may actively regulate the DC link voltages across the individual DC link capacitors. There are types of multi-cell power converters in which the first converter cells are connected in series between input nodes of the multi-cell power converter and in which the first converter cells are implemented such that during a start-up of the multi-cell power converter, the DC link capacitors are connected in series between the input nodes to form a capacitive voltage divider. During start-up, the first converter cells do not actively regulate the DC link voltages and a sum of the DC link voltages essentially corresponds to a peak of an input voltage received at the input. During normal operation, the DC link capacitors not only buffer electric energy received via the first converter cells from the input and forwarded via the second converter cells to the at least one output, but may also act as power supplies from which the first and second converter cells receive power required for a proper operation.
During the start-up, the first and second converter cells start to receive power from the DC link capacitors. The power consumptions of the individual converter cells may be different so that the individual DC link capacitors may be discharged differently. This may result in an imbalance of the DC link voltages during start-up. Such imbalance may include an increase of the DC link voltage of one or more DC link capacitors to above a voltage blocking capability of semiconductor devices implemented in the converter cells connected to the respective DC link capacitor(s). This may cause the semiconductor devices to be damaged or destroyed.
There is therefore a need to balance the DC link voltages in a multi-cell power converter during start-up.